It is best to speak out loud when tapping because the goal is to keep your mind focused on the issue at the same time you tap and that is usually easier to do aloud. However, in public places, or other times when it's not such a great idea to speak aloud, it's fine to just say the words silently to yourself. Same with tapping the points: It is generally best to use your hands, but when in public you can either use fewer points and see if you get a result, or you can tap all of them with your "imaginary fingers".